Anterior cervical plate holder/drill guide and method of use

ABSTRACT

A drill and tap guide system is disclosed which can be mounted on a bone plate to provide a finn foundation for accurately drilling and tapping screw holes into vertebra to be instrumented. The drill and tap guide system includes an assembly support which is engaged to the plate by way of a positioning screw and cross pins mounting the positioning screw to the guide body. A tap sleeve and drill guide can then be supported by the assembly support, which both thereby provide accurate positioning for a drill. In another embodiment, the system includes a guide apparatus for holding a spinal plate and drilling and tapping the bone. The guide comprises two arms which pivot with respect to each other and a foot attached at the end of each arm. Each foot has a hook which is adapted to securely grasp a spinal plate and a pair of thru-holes. Each hole is aligned with a screw bore in a spinal plate when the guide assembly is engaged to the plate. The system further includes a number of double-headed fixation pins, which hold the plate in position against the cervical spine during drilling and tapping.

This application is a continuation-in-part of application Ser. No.08/014,415 filed on Feb. 5, 1993 now U.S. Pat. No. 5,364,399.

BACKGROUND OF THE INVENTION

The present invention concerns spinal instrumentation systems, such asfor use with the cervical vertebrae. More particularly, the inventionpertains to a plating system for use in treatment of the cervical spine.

Within the last decade, the use of fixation plates for treatment ofspinal disorders or for fusion of vertebrae has grown considerably.While early procedures using fixation plates were at the lower lumbarlevels, spinal fixation plates have recently found applications in theinstrumentation of the cervical spine. Successful spinal instrumentationin this region is particularly difficult given the problems of safelyaccessing the instrumentation site.

The upper cervical spine can be approached either anteriorly orposteriorly, depending upon the spinal disorder to be treated. Many ofthe well known surgical exposure and fusion techniques of the cervicalspine are described in the publication entitled Spinal Instrumentation,edited by Dr. Howard An and Dr. Jerome Cotler, particularly at pages1-11. Of particular relevance to the present application are theexposure techniques and procedures for the anterior approach describedat pages 1-5 of this publication, which disclosure is incorporatedherein by reference. In this text, as well as in other documentationdescribing cervical spine surgical techniques, it is stressed thatcomplications associated with the procedure can be devastating, such asinjury to the brain stem, spinal cord or vertebral arteries. Inaddition, a lengthy procedure can lead to typical surgicalcomplications.

On top of the normal complications associated with exposure and fusionof the cervical spine, implantation of a spinal fixation plate adds tothe degree of risk and complication. In a cervical plating system ofSynthes, Inc., it is necessary to locate the fixation plate over thevertebral levels to be instrumented and use this plate as a drill guidefor drilling and tapping the bone in preparation for receiving afixation screw. The system and procedure provide for a soft tissueprotector in the manner of an elongated sleeve which is intended tominimize damage to the surrounding muscle and other tissues.

There is a need for a cervical plating system which minimizes theintrusion into the patient and reduces trauma to the surrounding softtissue. Moreover, a system is required that allows for easy access todrill and tap the cervical vertebrae with little room for error inpositioning the fixation screw.

Even as the cervical spine instrumentation techniques can be improved,so can the manner of fixation of the plate to the affected vertebrallevels. For example, the Synthes, Inc. locking plate accepts spinalscrews at several locations at the ends and in the middle of the plate.In each case, the screws are not capable of varying degrees of fixationbetween the vertebra and the plate. In addition, the Synthes deviceutilizes a locking screw which is threaded into the expansion head ofthe vertebral fixation screw to lock the screw into the plate. Thisprocedure requires a locking screw for every fixation screw, therebylengthening and complicating the procedure.

During anterior cervical surgery, alignment of the plate with thevertebral bodies and placement of the bone screws in the superior andinferior ends of the plate are often the most critical aspects of theprocedure. The surgeon must securely and rigidly hold a bone plateagainst the anterior surface of the vertebral bodies, visualize theplacement of the plate with fluoroscopy, obtain proper alignment, drill,tap and finally seat the bone screws. It is desirable to perform thesesteps using one instrument which firmly and consistently attaches to theplate in the stone manner every time.

There therefore remains a need for a cervical plating system whichprovides for a wider range of fixations at the different vertebrallevels. The need also extends to a plating system which minimizes thesteps required to provide firm fixation of the spinal screws to theplate. Other requirements for an optimum cervical fixation systemaddressed by the present invention are disclosed herein as thecomponents of the system are described.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, a system for anteriorfixation of the spine includes an elongated fixation plate having alongitudinal axis and a length along the axis sufficient to span betweenat least two vertebrae. The plate includes a lower surface adapted toengage the anterior portion of the vertebrae and an opposite uppersurface, as well as opposite first and second ends. A pair of screwbores are defined at both of the first and second ends between the lowerand upper surfaces and displaced from each other transverse to thelongitudinal axis of the plate. The pair of screw bores have centerlinesthat diverge relative to each other and relative to the lower surface ofthe plate. The system also includes several bone engaging screws, oneeach for each of the pair of screw bores at both of the first and secondends. Each of the screws includes em elongated shank with bone engagingthreads and an enlarged head for engaging a corresponding one of thescrew bores at the upper surface of the plate when the shank extendstherethrough.

The divergent screw bores achieve one object of the invention tominimize the intrusion and trauma to tissue surrounding the implantationsite. As the bores diverge below the plate, they converge above theplate so that two screws can be inserted through the bores at an end ofthe plate from essentially the same location. This improvement reducesthe amount of tissue that must be retracted in order to provide accessto the screw bores in the fixation plate. In one specific embodiment,the the centerlines of the pair of screw bores diverge relative to eachother at an angle of about ten (10) degrees.

In a further aspect of the invention, the lower surface of the plate iscurved transverse to the longitudinal axis to conform to the anteriorsurface of a vertebra and is curved along the longitudinal axis toconform to the lordotic curvature between the vertebrae. This featureeliminates having to bend the fixation plate at the surgical site duringthe instrumentation procedure.

To enhance the versatility of the spinal fixation system of the presentinvention, the fixation plate includes a number of elongated slotsdefined in the plate between the lower and upper surfaces disposedlongitudinally between the number of screw bores at both ends of theplate. Each of the number of elongated slots has mutually parallel slotaxes along their length that intersect the longitudinal axis of theplate at an acute angle. Additional bone engaging screws are providedfor engaging intermediate vertebrae through one of the elongated slots.Preferably, the slots are arranged on the plate such that the ends ofadjacent slots overlap each other transverse to the longitudinal axis ofthe plate.

One important component of the preferred embodiment of the invention isscrew fixation means for clamping the head of the bone screws to theplate. Pursuant to this invention, the screw fixation means engaging theplate at its upper surface to clamp the bone screw heads within recessesin the plate. Preferably, the bone screws and the screw fixation meansare configured to reside within recesses in the plate so that thesecomponents are flush with or below the upper surface of the plate. Thisaspect realizes an advantage over prior systems which include componentsprojecting above the fixation plate, leading to irritation and trauma ofthe surrounding tissue.

In one specific embodiment, the screw fixation means includes a fixationbore defined in the plate at each of the first and second ends betweenthe screw bores. A locking screw is provided having a shank adapted tobe received within the fixation bore and an enlarged head adapted tosimultaneously cover a portion of the head of both screws receivedwithin the pair of screw bores. In another embodiment, the screwfixation means contemplates screw bores and screw shanks that arecomplementary tapered at a MORSE™ taper. The integration of the MORSE™taper enhances the degree of fixation between screw and plate,particularly when combined with the locking screw.

Still another embodiment of the screw fixation means is contemplatedthat includes a groove formed in the screw bores at the lower surface ofthe plate. The bone engaging screws include a corresponding groovedefined in the shank of the screw between the head of the screw and thebone engaging threads. An O-ring is provided that has an outer diameteradapted to be retained within the groove in the plate and an innerdiameter adapted to be retained within the groove in the shank of thebone screws. When the bone screw is mounted within the screw bore, theO-ring retains each of the bone screws within the bore without thenecessity of a locking screw. However, the degree of rigidity of thisfixation is less than the rigidity provided by the locking screwapproach outlined above.

The invention further concerns an improved system for separatelydrilling fixation holes into vertebrae to be instrumented with a spinalplate. In one specific embodiment, the system includes a spinal platewith a number of screw bores adapted to receive spinal screwstherethrough. A pin bore is also defined through the plate adjacent eachof the number of screw bores. A drill guide is provided which includes aguide body having a lower surface configured for juxtaposition with theupper surface of the spinal plate and defining a guide bore and a secondpin bore therethrough. The guide bore and the second pin bore arearranged to align with one of the number of screw bores and the pinbore, respectively, in the spinal plate when the guide body isjuxtaposed with the plate.

The system further includes a pin adapted to be received between thespinal plate and the guide body within the pin bore and the second pinbore, respectively. The pin is rigidly engaged at one end to the guidebody and at the opposite end to the spinal plate to accurately positionand retain the guide body relative to the plate. An elongated sleevehaving one end configured to be received within the guide bore of theguide body, and a drill bore therethrough is provided for integratinginto the guide body. An elongated drill extends through the drill boreof the elongated sleeve.

In another embodiment the system includes a guide apparatus for holdinga spinal plate and drilling and tapping the bone. The guide comprisestwo arms which pivot with respect to each other, a handle and two feetattached to the ends of the arms. Each foot has a hook integrallyattached to the edge of the foot which is adapted to securely grasp aspinal plate. Each foot also has a pair of thru-holes. Each holecorresponds to screw bores in a spinal plate when the guide assembly isattached to a spinal plate. The system further includes a number ofdouble-headed fixation pins. The diameter of the first head is greaterthan the diameter of the thru-holes in the feet. The diameter of thesecond head is smaller than the thru-holes but greater than the screwbores in the spinal plate. The fixation pins serve to hold the plate inposition against the cervical spine during fluoroscopy and drilling andtapping. The system also contains a drill-tap sleeve having a stopmember. The outside diameter or the sleeve is slightly smaller than thethrough holes in the feet. The system is intended to be used with adrill bit having a stop member.

The present invention provides many advantages and benefits over priorart anterior plating systems. One benefit is that the plating system ofthis invention minimizes the amount of intrusion at the instrumentationsite. Another advantage is achieved by the reduced number of componentsrequired to achieve rigid fixation of the bone screws to bone and plate.

A further benefit resides in the smooth outer contour of theinstrumentation once they are implanted that is accomplished by platerecesses and other aspects of the invention. The bone screws and screwfixation means are safely retained flush with or below the surface ofthe plate to remove this potential source for irritation and trauma tothe surrounding tissue.

Other benefits, advantages and objects of this invention will becomeapparent to a person of skill in the field of spinal instrumentationupon consideration of the following written description and accompanyingfigures.

FIG. 1 is a representation of the upper cervical spine instrumented withthe cervical plating system in accordance with one embodiment of thepresent invention.

FIG. 2 is a top elevational view of a cervical plate in accordance withone embodiment of the invention as depicted in FIG. 1.

FIG. 3 is a side cross-sectional view of the plate shown in FIG. 2 takenalong line 3--3 as viewed in the direction of the arrows,

FIG. 4 is an end cross-sectional view of the plate shown in FIG. 2 takenalong line 4--4 as viewed in the direction of the arrows.

FIG. 5 is an end cross-sectional view of the plate, similar to the viewin FIG. 4, showing the plating system with the fixation screws partiallythreaded into the vertebra just before being firmly affixed to thecervical plate.

FIG. 6 is an end cross-sectional view similar to the view in FIG. 4showing an alternative embodiment of the plate and fixation screw.

FIG. 7 is an end cross-sectional view similar to FIG. 4 showing yetanother embodiment of the plate and fixation screw of the presentinvention.

FIG. 8 is a top elevational view of an alternative embodiment of thefixation plate.

FIG. 9 is a top elevational view of still another alternative embodimentof the fixation plate in accordance with the present invention.

FIG. 10 is an exploded view of a drill and tap guide assembly inaccordance with the present invention used in connection with thefixation plates of the previous figures.

FIG. 11 is a top view of the assembly support of the drill and tap guideassembly shown in FIG. 10, as viewed in the direction of the arrows online 11--11, in which the cross pins are shown prior to insertion intothe assembly support.

FIG. 12 is a side elevational view of the positioning screw shown inFIG. 10.

FIG. 13 is a side elevational view of the drill and tap guide assemblyas arranged during a typical drill and tap operation.

FIG. 14 is a front cross-sectional view of the plate holder-drill guideassembly.

FIG. 15 is a side cross-sectional view of the guide assembly.

FIG. 16 is a top view of the feet shown in FIG. 14, as viewed in thedirection of the arrows on line 16--16.

FIG. 17 is a elevational view of the holder engaged to a bone plate.

FIG. 18 is a side cross-sectional view of the double-headed pin.

FIG. 19 is an exploded view of a guide assembly in accordance with thepresent invention used in connection with the fixation plates of theprevious figures.

FIG. 20 is a side cross-sectional view of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended, such alterations and furthermodifications in the illustrated device, and such further applicationsof the principles of the invention as illustrated therein beingcontemplated as would normally occur to one skilled in the art to whichthe invention relates.

In accordance with one embodiment of the invention, an elongatedfixation plate 20 is instrumented to upper cervical vertebrae C₁ -C₄, inparticular between the C₃ and C₅ vertebrae. Such an arrangement mayarise where the C₄ vertebrae requires fusion or to address a problemwith the discs between these vertebrae. It is understood, of course,that while FIG. 1 depicts instrumentation between the C₃ and C₅vertebrae, instrumentation at other vertebral levels is contemplated bythe present invention. By general introduction to the components of theinventive system, the fixation plate 20 is engaged to the variousvertebrae by way of a number of bone engaging screws 30. Screw fixationmeans 40 is provided to firmly and rigidly fix certain of the boneengaging screws to the plate.

Referring now to FIGS. 2-4, details of the construction of fixationplate 20 can be discerned. The plate 20 includes a lower surface 21which is oriented adjacent the vertebra, and an opposite upper surface22, as well as a first end 23 and an opposite second end 24. A bridgeportion 25 spans between the two ends of the plate.

The plate 20 or the present embodiment includes a number of screw bores27 defined in the plate. In the preferred embodiment, two screw boresare oriented at each of the first end 23 and the second end 24. Thus,four such screw bores are included so that fixation screws mounted inthe plate through these bores provide a solid quadrilateral fixation tothe instrumented vertebrae. Each of the bores 27 includes a sphericallyshaped recess 28 defined from the upper surface 22 of the plate, asshown more clearly in FIG. 4. As discussed in more detail herein, therecess 28 is adapted to receive and substantially conceal the head of afixation screw extending through the bore.

Referring again to FIG. 4, it can be seen that the screw bores 27 at oneend of the plate, such as end 24, are each cut at axes A₁ and A₂. Theseaxes converge above the upper surface 22 of the plate at an angle D,which provides a significant benefit over prior systems. In priorcervical fixation plates, the axis of the screw bores are generallyperpendicular to the curved plate surface, as in the Synthes cervicalplate. With the curvature of the plate, the axes of the screw bores atwhich the screws must be inserted are divergent relative to thevertebra. This means that more soft tissue must be retracted around theinstrumentation site in order to allow the fixation screws to be passedthrough the screw bore and threaded into the vertebra. On the otherhand, in accordance with this aspect of the present invention, theconvergent angle D between the two screw bores 27 at each end of theplate provide for insertion of the fixation screws from generally thesame location above the plate. In this instance, less soft tissue needsto be retracted in order to allow the surgeon to pass a fixation screwthrough the plate and into the vertebra. In one specific embodiment, theangle D between the screw bore axes A₁ and A₂ is about ten (10) degrees.It has been found that this angle provides adequate purchase for thescrews into the vertebrae, while allowing streamlined entry of thescrews at the implant site.

As shown more clearly in FIGS. 3 and 4, the plate 20 is formed to definespecific curvature in two directions. As seen in FIG. 4, the lowersurface 21 of the plate is curved about a radius R which corresponds tothe curvature of the anterior surface of a vertebra. This form ofcurvature is generally known in the art, such as evidenced by theSynthes plate. For cervical vertebrae, a radius R₁ of about 3.80 mm(1.50 inches) is acceptable. However, in accordance with the presentinvention, the lower surface 21 of the fixation plate 20 is also curvedalong its length at a radius R₂, as shown in FIG. 3, to correspond tothe lordotic curvature of the cervical spine. Plates such as the Synthesplate must be bent at the time of surgery, if at all. It has been foundthat forming the fixation plate 20 with the lordotic curvature radius R₂in the lower surface 21 of the plate eliminates unnecessary activity bythe surgeon during the procedure and reduces any bending stresses thatmay be inherent in the plate when it is bent at the surgical site. Incervical vertebra applications, a radius of about 18.4 mm (725 inches)accommodated the cervical lordotic curvature.

Referring now to FIG. 5, the details of the bone engaging screws 30 andthere interface with the fixation plate 20 are shown. Each bone engagingscrew 30 includes an elongated shank 31 having a lower threaded portion31b and an upper smooth portion 31a. Adjacent the smooth portion 31a isan enlarged head 32 of the screw. The head 32 includes a truncatedspherical upper surface 33a and an opposite spherically cut lowersurface 34. The lower surface 34 is curved to match the curvature of thespherical recess 28 of the screw bores 27 in the plate 20. The uppersurface 33 is truncated to provide a flat face, and defines a drivingtool recess 35 formed therein. The driving tool recess is adapted toengage a standard driving tool, such as an allen head tool frequentlyused to thread bone screws into a vertebra.

One important aspect of the screw 30 in accordance with the presentinvention resides in the configuration of the upper surface 33 of thehead 32. The truncated spherical aspect of the head allows substantiallythe entire screw head 32 to rest entirely within the screw bore recess28. In this manner, a portion of the screw head 32 is substantiallyflush with the upper surface 22 of the plate, while the remainder of thescrew resides below the upper surface within the recess 28. In FIG. 5the bone engaging screws 30 are shown just prior to being completelyfixed within the fixation plate 20. FIG. 6, while showing an alternativeembodiment of the bone screw, accurately depicts the flush mountedaspect of this invention. The particular angle of the screw bores axesA₁ and A₂ require a cutback of the top surface of the enlarged screwhead 32. While in the preferred embodiment this upper surface is atruncated spherical surface 33a, it is contemplated that the head 32 cansimply include beveled perimeter, provided that the cutback of the head32 is sufficient to allow the head to be substantially flush or belowthe upper surface 22 of the fixation plate 20.

As with other cervical implant systems, the present inventioncontemplates some means for fixing the bone engaging screws 30 to thefixation plate 20 to prevent the screws from working loose over time.Consequently, the system includes a screw fixation means 40, depictedbest in FIGS. 4 and 5. In one embodiment of the invention, the screwfixation means 40 includes a threaded fixation bore 41 formed in theplate 20 between the two screw bores 27 at each end of the plate. Thefixation bore 41 includes a recessed bore 42 defined from the uppersurface 22 of the plate, as shown more particularly in thecross-sectional view of FIG. 4.

As can be seen from FIGS. 2 and 4, the fixation bore 41, andparticularly the recessed bore portion 42, share an overlap 43 with thescrew bores 27. The necessity for this overlap is revealed in in FIG. 5which shows a second component of the fixation means 40, the lockingscrew 45. The locking screw 45 includes a threaded stem 46 which isconfigured to engage the threaded bore 41 in the plate 20. The lockingscrew 45 includes a flat head 47 which is thin enough to reside entirelywithin the recessed bore portion 42 in the plate so that the lockingscrew is not exposed above the upper surface 22 of the plate. The head47 includes a pair of driving tool bores 48 which are configured toreceive a pin type driving tool for threading the locking screw 45 intothe fixation bore 41. Other configurations, such as an allen headrecess, are contemplated to permit threading the locking screw 45 intothe fixation bore 41.

The locking screw 45, particularly at the overlap 43, contacts each ofthe bone engaging screws 30 situated within the screw bores 27.Typically, the bone engaging screws 30 would already be threaded fullyinto the vertebra so that the lower head surfaces 34 of the screws arein direct contact with the spherical recess 28 the plate. (The screwsare shown slightly backed out in FIG. 5 to allow mode completevisualization of the features of this invention.) In addition, the lowersurface 21 of the fixation plate 20 would normally be pressed to contactwith the vertebra. In this configuration, the locking screw 45 is driveninto the fixation bore 41 until the head 47 contacts and firmly clamps aportion of the head 32 of both bone engaging screws 30 at the overlap43.

The addition of the fixation means 40 and locking screw 45 provides ameans for rigidly fixing the bone engaging screws 30 to the fixationplate 20. Specifically, the bone engaging screws 30 are highlyrestricted in their ability to wobble or rotate within the recess 20 ofthe screw bore 27 when clamped by the locking screw 45. The screwfixation memos 40 of the present invention provides a unique method forfixing two bone engaging screws at one time. Prior techniques requiredindividual means for fixing each screw separately, which complicated theprocedure and added additional instrumentation to the implant. On theother hand, the fixation means 40 of the present invention greatlystreamlines the process of rigidly fixing the bone engaging screws 30 tothe plate 20. In accordance with a typical procedure, once theappropriate openings have been drilled and tapped into the vertebra, theplate 20 can be positioned against the vertebra and the bone engagingscrews 30 be driven into the bone through the screw bores 27 in theplate. Once the screws 30 have been driven to the proper depth andtorque the locking screw 45 of the screw fixation means 40 can be firmlythreaded into the fixation bore 41 to clip the head 32 of each of thebone screws 30 within their respective recesses 28.

Attention is now redirected to FIGS. 1-3 for explanation of a furtherfeature of the fixation plate 20 of the present invention. In accordancewith one embodiment of the invention, the plate 20 includes a slot 50formed within the bridge portion 25 of the plate. The slot 50 has aconcave surface 51 formed like the spherical recesses 28 of the thescrew bores 27 to accept the head 32 of a bone engaging screw 30 aspreviously described. In accordance with the invention, the slot 50, orthe axis S along the length of the slot, is oriented at an acute angle Tto the longitudinal axis L of the fixation plate 20. This diagonal slot50 provides means for supporting an added bone screw between the twoinstrumented vertebrae fixed at the ends of the plate.

Unlike the bone engaging screws passing through the screw bores 27 atthe ends of the plate 20, a screw extending through the diagonal slot 50preferably does not include any means for rigidly fixing the head of thescrew to the plate. Thus, only a "semi-rigid" fixation is providedbetween a screw within the slot 50 and the spanned vertebra. Althoughrigid fixation is essential at the ends of the plate to keep the platefirmly engaged to the vertebrae, non-rigid fixation of the intermediatescrew passing through the slot 50 is all that is required and is in factdesired to avoid complications following the instrumentation of thevertebrae.

The orientation of the slot 50 at its acute angle T allows the bridgeportion 25 of the plate to be cut back somewhat to reduce the incursioninto surrounding tissue and the associated trauma. In particular, thesidewalls 26 of the bridge 25 can be cut parallel to the slot wallsprovided sufficient material is maintained to support the slot andprevent fracture of the plate at the slot. Similarly, sufficientmaterial must be located around the screw bores 27 at the ends of theplate to provide a sufficiently strong plate. One object of theinvention is to reduce the amount of trauma to surrounding tissue, aswell as the amount of space required for the plate when it is affixed tovertebrae. Cutting the plate contours, such as the sidewalls 26 of thebridge portion 25, in the manner shown achieves these purposes, whilealso reducing the amount of material used to make the plate.

A further embodiment of the invention includes a fixation plate 55illustrated in FIG. 6. The fixation plate 55 includes a lower surface 56configured to contact the surface of a cervical vertebra. As with thefixation plate 20 of the previous embodiment, the plate 55 includes apair of screw bores 57 at each end of the plate. Each screw bore 57includes a spherical recess 58 adapted to receive a bone engaging screwsimilar to screw 30.

The fixation plate 55 differs from the previous plate 20 in the mannerof fixing the bone engaging screws to the plate. In particular, theplate 55 does not include a locking screw 45 or fixation bore 41 asshown in FIG. 5. Instead, the screw fixation means 59 of this embodimentcontemplates modifications to the bone screw and to the plate.Specifically, the fixation means 59 includes a lower circular recess 60defined in the screw bore 57 at the lower surface 56 of the plate. Amodified bone engaging screw 62 is provided which includes an elongatedshank 63 having bone engaging threads. The head of the bone screw 64 isconfigured similar to the head 32 of the bone engaging screws 30 so thatthe screw can be situated flush with or below the upper surface of thefixation plate 55, with the lower surface 65 of the head 64 in contactwith the spherical recess 58.

The bone engaging screw 62 includes a smooth shank portion 67 betweenthe threaded shank 63 and the head 64. A groove 68 is defined in thesmooth shank portion 67 immediately below the screw head 64. The groove68 is configured to receive an O-ring 69 which is trapped between thegroove 68 and the lower recess 60 in the fixation plate 55. Preferably,the O-ring is formed of a biocompatible elastomeric material that isstrong enough to resist screw pull out. In particular, any outwardmovement of the bone screw is resisted by the pressure transmittedbetween the recess 60 and the groove 68 and the bone screw through theO-ring 69.

Yet another embodiment of the cervical fixation plate is shown in FIG.7. In this embodiment, a fixation plate 70 includes an upper surface 71and an opposite lower surface 72. A pair of screw bores 74 are definedthrough the plates at the same angles as the bores 27 in the embodimentshown in FIGS. 1-4. In addition like the embodiment shown in FIG. 5, ascrew fixation means 75 incorporating a locking screw is included tohelp clamp the bone screw to the plate. However, in a modification fromthe previous embodiments, the screw bore 74 is tapered at an includedangle M. This taper M converges from the upper surface 71 to the lowersurface 72. Also included in this embodiment is a bone engaging screw 77which tapers at an included angle N. The two angles M and N are MORSE™taper angles of preferably 2-3 degrees. This MORSE™ taper angles areknown in machine design to form a tight engagement between componentswhen both are cut at a MORSE™ angle. The bone engaging screw 77 includesa threaded portion 78 and head portion 79. At least the head portion 79of the bone engaging screw 77 is tapered at the MORSE™ taper N to firmlyfix within the MORSE™ taper M of the screw bore 74. The interfacebetween the two MORSE™ tapers add a higher degree of fixation of thebone engaging screw 77, particularly when combined with the screwfixation means 75.

In order to provide a broad range of plates for fixing to the cervicalvertebra to address a variety of spinal problems, a number of differentspinal plates can be provided with a complete cervical fixation system.Two such alternative plates are shown in FIGS. 8 and 9. The first plate80 is a nearly square plate having the two screw bores 27 at theopposite ends of the plate along with the fixation bore 41 to receive ascrew fixation means 40 as previously described. However, in thisembodiment, the slot 50 of the previous plate is eliminated in favor ofa single bore 81. This single bore does not allow the variability ofposition of the fixation screw relative to the rigid fixation screws,but it does provide means for a non-rigid engagement to the plate.

The fixation plate 85 shown in FIG. 9 is substantially like the plate 20shown in FIG. 1 with the addition of several parallel slots.Specifically, slots 86-89 are included in the bridge portion 90 of theplate. Again as with the plate 20, the sidewalls 21 of the bridgeportion 90 are cut at the slot angle to achieve the functions describedabove. With the plate 85 of this embodiment of the invention, a numberof slots allow the fixation plate to span across a number of cervicalvertebrae. The ends of each successive plate laterally overlap so that asingle intermediate vertebra can be instrumented with two bone screwsextending through two different slots, such as consecutive slots 86 and87. As also seen in FIG. 9, the length of the slots 86 and 89 is greaterthan the length of slots 87 and 88, principally because the slots 87 and88 are situated within the middle of the bridge portion 90. In order toallow sufficient material around the slots, the middle of slots 87 and88 cannot have the same length as the end slots 86 and 87.

Also included with the cervical plating system of the invention is adrill and tap guide assembly 100, the details of which are described inconnection with FIGS. 10-13. It should first be appreciated that intypical prior art systems the fixation plate itself serves as the guidefor drilling the hole locations in the vertebra to receive the fixationscrews. Currently, no instruments or procedure exists which allows thesurgeon to securely and rigidly hold an anterior cervical plate againstthe anterior surface of the vertebral bodies, utilize fluoroscopy,obtain proper alignment, drill, tap and finally seat the bone screws allutilizing the same instrument without this instrument being removeduntil all implantation steps are complete. For example, in the Synthescervical spine plating system, a plate positioner holds the plate inposition on the vertebra while each screw hole is being drilled. A softtissue protector is provided which surrounds the drill and which isseated within the screw bores in the plate. Consequently since a portionof the tissue protector sheath is situated within the screw bore, thediameter of the drill and tap that can pass through the bore mustnecessarily be noticeably smaller than the bore itself. This means thatthe tap hole in the bone is smaller than the bone screw to be fixed intothe vertebra, rendering threading the bone screw more difficult than ifthe tap were closer to the diameter of the bone screw itself. The drilland tap guide assembly 100 of the present invention eliminates thisdifficulty. In addition, the tap guide provides for virtually error freepositioning of the drill and tap holes in the vertebra, which cannot bereadily accomplished by the essentially cantilevered supported softtissue retractor sheath in the prior art devices. The drill and tapguide assembly 100 includes several components, such as the assemblysupport 101, the sleeve 102, the drill guide 103, the drill 104, apositioning screw 105 and cross pins 106.

The assembly support 101 includes a guide body 110 which is asubstantially solid block with a contoured lowered surface 111 adaptedto fit the contour of the upper surface 22 of a fixation plate 20, (suchas the plate shown in FIG. 1). The guide body 110 includes an integralflange 113 extending beyond one side and bottom edge of the body. Inparticular, the flange 113 is adapted to engage an end face 24 of theplate 20, as shown more particularly in FIG. 13. This flange 113 assistsin properly positively positioning the drill guide assembly 100 relativeto the plate 20 and the vertebra. The guide body 110 includes a pair ofguide bores 115 and 116, which bores are lined to coincide with the axesA₁ and A₂ of the fixation screw bores 27 in the plate 20. Thus, with theguide body 110 resting on top of the upper surface 22 of the plate, thetwo guide bores 115 and 116 should substantially align and coincide withthe fixation screw bores 27 at one end of the plate 20.

The guide body 110 is engaged to the plate 20 in a unique fashion. Forthis engagement, the guide body includes a positioning screw bore 118which is centrally located between the two converging guide bores 115and 116. The positioning screw bore 118 is adapted to receive a portionof a positioning screw 105 therein. The details of the positioning screware shown in FIG. 12. In the preferred embodiment, the positioning screw105 includes a head 125 which is threaded to to engage the threadedfixation bore 41 in the plate 20. (The fixation bore 41 is used also forengaging the locking screw 45 as part of the screw fixation means 40, asdescribed above). Extending from the threaded head 125 is a stem 126which has a driving tip 127 at its end. The driving tip includes atransverse slot 128 that is adapted to receive a driving instrument,such as a screwdriver to allow the threaded head 125 to be screwed intothe fixation bore 41 of the plate 20. The positioning screw furtherincludes a contoured portion 129 of the stem which is adapted to providea locking surface for cross pins 106. As shown in FIGS. 10 and 11, crosspins 106 are extended through cross pin bores 120 which passperpendicularly to the positioning screw bore 118. The cross pins boresoverlap both with the positioning screw bore 118 and a corresponding oneof the guide bores 115 or 116, such as shown in the overlap 121 in FIG.11.

The importance of these various components can be appreciated bydescription of the manner in which the assembly support 101 is affixedto the fixation plate 20. In particular, in one manner of using theassembly support, the threaded head 125 of the positioning screw 105 isthreaded into the fixation bore 41 of the plate 20 with the stem 126projecting upward away from the top surface 22 of the plate. Thepositioning screw 105 is initially loosely threaded into the bore. Theguide body 110 is then placed over the positioning screw 105 with thescrew extending through the positioning screw bore 118 in the center ofthe body. The flange 113 helps locate the guide body 110 with respect tothe edge 24 of the plate, and more particularly with respect to thescrew bores 27 at the end of the plate. With the guide body 110 mountedover the positioning screw 105, the cross pins 106 are pushed throughthe cross pin bores 120 on either side of the positioning screw 105. Thecross pins thus contact the contoured portion 129 of the positioningscrew stem 126. The guide body 110 is then at least initially connectedto the plate 20 by way of the positioning screw 105 and the cross pins106 which engage the positioning screw. At this stage, however, theengagement between the guide body 110 and the plate 20 is not tight,awaiting the next step for completing the drill and tap guide assembly100. The positioning screw bore 118 allows access for a driving tool toengage the driving tip 127, and particularly the slot 128, of thepositioning screw 105, to tightly thread the screw into the threadedbore 41 when the assembly is complete.

The assembly 100 further includes a tap sleeve 102 that includes asleeve body 130 defining a drill guide bore 131 therethrough. At one endof the sleeve body 130 is an end taper 132, which can be generallyconfigured to engage the spherical recess 28 of the screw bore 27 in theplate 20. The other end of the sleeve body 130 includes an enlarged stop133. Nominally, the sleeve body 130 has a diameter slightly smaller thanone of the guide bores 115 or 116, while the stop 133 has a diameterlarger than these bores. With the addition of the tap sleeve 102, theengagement between the assembly support 101 and the plate 20 can becompleted. Once the guide body 110 is preliminarily positioned andattached to the plate by way of the positioning screw 105 and cross pins120, the sleeve body 130 can be passed through one of the guide bores,such as guide bore 115, until the tapered end 132 of the sleeve body 130contacts the spherical recess 28 in the plate 20. As the sleeve body 130passes through the bore 115, the outer surface of the sleeve pressesagainst one of the cross pins 106, which cross pin firmly pressesagainst the stem portion 129 of the positioning screw 105. This providesa solid engagement of all of the components of the drill and tap guideassembly from the tap sleeve 102 to the plate 20. While the cross pin106 presses against the positioning screw 105, it also presses backagainst the sleeve body 130 to provide some clamping force to hold thesleeve within the guide body 110.

With these components of the drill and tap guide assembly 100 firmlyengaged, it is now possible to pass the drill guide 103 through the bore131 in the tap sleeve body 130. The drill guide body 135 includes adrill bore 136 adapted to receive the drill 104 therethrough. The body135 also includes a stop 137 which is larger than the drill guide bore131 in the tap sleeve body 130, to prevent the drill guide from passingcompletely through the tap sleeve body. The final arrangement of thecomponents is shown in the side view of FIG. 13. In this view it can beappreciated that the flange 113 helps locate the guide body 110 relativeto the plate so the drill bores 131 and screw bores 27 align. The guidebody 110, when fixed to the plate 20 by the positioning screw 105 andcross pins 106, provides a solid and accurate location for the tapsleeve 102, the drill guide 103 nested within the tap sleeve, andultimately the drill 104 passing through each of these components. Itcan certainly be appreciated that the drill and tap guide assembly 100of the present invention provides a firm foundation and accuratelocation for drilling and tapping holes in the vertebra at the properlocation relative to the fixation plate 20. The assembly 100 of thepresent invention still utilizes the fixation plate 20 as a template forlocating the screw holes. However, the assembly 100 provides a firmerfoundation for performing the drilling and tapping operation than anyknown prior art device.

A further embodiment of the invention is shown in FIGS. 14-19. In thisembodiment, the system includes a holder-drill guide 150, double-headedfixation pins 170, a drill-tap sleeve 180 having a stop member 181, adrill bit 182 having a stop member 183, a bone screw tap (not shown),bone screws 30 and a bone plate 20. The guide includes two feet 157, twoarms 151, 152, a locking mechanism 153 and a handle 162. Each footdefines a pair of thru-holes 158 which are aligned with the screw bores27 when the bone plate 20 is engaged to the guide 150. A small hook 161on each foot 157 of the guide attaches to a notch 159 on each end of theplate 20. The locking mechanism 153 is then tightened to firmly attachthe guide 150 to the plate 20. Double-headed fixation pins 170, as shownin FIG. 18, are provided to temporarily attach the entire guide-plateassembly to the bone. The pins 170 include a first head 171, having adiameter larger than the diameter of the thru-holes 158 of the feet 157,a second head 172 having a diameter smaller than the diameter of thethru-holes 158 but larger than the screw bore 27 in the plate 20. Thefirst head 171 and the second head 172 are connected by a neck portion173. The fixation pins 170 also include a shaft 174 attached to thesecond head 172 and tapering to a point 175. Referring to FIG. 19, thefirst head 171 of the pin 170 sits above the foot 157, while the neckportion 173 extends through the thru-hole 158, the second head 172 restsin the spherical recess 28 and the shaft 174 and pointed portion 175extend through the screw bore 27 and into the bone. One pin 170 will beplaced in one of the two holes 158 in each foot 157 of the guide, thusholding the plate 20 in position against the cervical spine while finalpositioning can be verified with fluoroscopy.

Referring to FIG. 19, a screw is seated in each unused screw bore 27 inboth ends 23, 24 of the plate 20 in this manner: The drill-tap sleeve180 is placed in the unused hole in each end of the guide 150. A drillbit 182 with stop 183 is then used through the sleeve 180 followed by abone screw tap with a stop (not shown). The sleeve 180 is then removedand a bone screw 30 is placed through the same hole in the foot 157 ofthe guide 150. After the screw 30 is tightened down, it rests in thespherical recess 28 in the end 23, 24 of the plate 20.

After one bone screw 30 is placed in each end 23, 24 of the plate 20,the fixation pins 170 are removed and a sleeve 180 is placed in each ofthese holes, and the process is repeated until two screws 30 are firmlyattaching each end of the plate 20 to the cervical spine. At this point,the locking mechanism 153 is loosened and the guide 150 is removed.

It is important to note that this guide can be made adjustable to covera wide range of plate lengths. The arms 151, 152 of the guide 150 arepivotally attached to each other by way of a pivot bolt 160. The degreeof the angle formed by the two arms 151, 152 is adjusted by a lockingmechanism 153. The locking mechanism 153 includes a locking rod 155,pivot pins 156 and an adjustment knob 154.

Referring now to FIGS. 14 and 17, the locking rod 155 extends throughthe pivot pins 156. The locking rod 155 is provided with an externalthreaded surface and the pivot pins 156 are provided with a matinginternal threaded surface. The threaded surfaces mesh so that when thelocking rod 155 is turned by way of the adjustment knob 154, the turningaction of the locking rod 155 pushes the two pivot pins 156 in oppositedirections thereby increasing or decreasing the angle between the arms151, 152, and providing or relieving a clamping force on the plate 20.

Referring now to FIG. 16 each foot 157 defines two cut out attachmentpoints 166. Each arm 151, 152 is provided with two attachment fingers164, as shown in FIGS. 14 and 15 which are attached to the attachmentpoints 166 of each foot 157 by way of a dowel 165. The feet 157 are thuspivotally attached to the arms 151, 152 to adapt to plates 20 of variouslengths and curvatures.

FIG. 19 shows a drill bit 182 and drill sleeve 180. A bone tap (notshown) would also fit through the sleeve 180 to prepare the drilled holefor the bone screw 30. This sleeve 180 must be removed for the bonescrew 30 to fit through the foot 157 of the guide 150 although thesystem could be designed such that the bone screw 30 and screwdriverthemselves also fit through the sleeve 180. This would mean the sleeve180 would not be removed until the bone screws 30 have been firmlyaffixed to the plate 20 and bone.

In an alternative embodiment 190 shown in FIG. 20, the configuration ofthe guide 190 increases the surgical view of the implant. The bridgeportion 163 is attached to the arm 191 at a 90° angle. The arm 191 isslightly bent at a point 192 and is provided with a wrist 193. In thisconfiguration, the guide 190 does not obstruct the view of the surgicalworksite.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the stone is to be considered asillustrative and not restrictive in character, it being understood thatonly the preferred embodiments have been shown and described and thatall changes and modifications that come within the spirit of theinvention are desired to be protected.

What is claimed is:
 1. A holder drill guide tool for accurately drillingfixation holes into vertebrae to be instrumented with a spinal platehaving screw bores, comprising:a first arm and a second arm, said firstarm attached to said second arm, each said arm having a proximal end anda distal end; a first foot attached to the proximal end of said firstare and a second foot attached to the proximal end of said second arm,each said foot defining a number of thru-holes sized to receive adrilling tool, each said hole being disposed in alignment with a screwbore in the spinal plate when the tool is engaged to a spinal plate; ahook attached to each said foot, said hook defining a surface forengaging an edge of the spinal plate; and a locking mechanism configuredto lock said feet in a position relative to each other to engage thespinal plate between said hook of each said foot with said thru-holesaligned with the plate screw bores.
 2. The holder drill guide tool ofclaim 1, wherein:said arms are pivotally attached at a pivot; and thelocking mechanism includes a threaded rod threadedly engaged betweensaid first and second arms apart from said pivot, whereby said armsrotate about said pivot as said threaded rod is rotated, to thereby varythe relative position of said feet.
 3. The holder drill guide tool ofclaim 2, wherein the second arm is shorter than the first arm and ispivotally attached to the first arm at a pivot point by a pivot bolt. 4.The holder drill guide tool of claim 1, wherein said feet are pivotallyattached to said arms.
 5. A system for accurately drilling fixationholes into vertebrae to be instrumented with a spinal plate,comprising:a spinal plate having a lower surface adapted to engage avertebra and an opposite upper surface and including;a number of screwbores defined through said plate between said lower and upper surfacesand adapted to receive spinal screws therethrough; and a fixation boredefined through said plate adjacent said number of bores; a drill guideincluding;a guide body having a lower surface configured forjuxtaposition with said upper surface of said spinal plate and defininga guide bore and a positioning screw bore therethrough, wherein saidguide bore is arranged to align with one of said number of screw boresand said positioning screw bore is arranged to align with said fixationbore when said guide body is juxtaposed with said spinal plate; apositioning screw adapted to be received between said spinal plate andsaid guide body within said fixation bore and said positioning screwbore; said positioning screw bore having means for rigidly engaging oneend of said positioning screw to said guide body; and said fixation borehaving means for rigidly engaging an opposite end of said positioningscrew to said spinal plate.
 6. The system of claim 5 further comprisingan elongated sleeve having a first end configured to be received withinsaid guide bore of said guide body, said sleeve having a drill boretherethrough.
 7. The system of claim 6, further comprising an elongateddrill having a shank configured to be rotatably received within saiddrill bore in said elongated sleeve, and further having a drill tip fordrilling into bone.
 8. A system for accurately drilling fixation holesinto vertebrae to be instrumented with a spinal plate, comprising:aspinal plate having a lower surface adapted to engage a vertebra and anopposite upper surface, the plate including:a first end and a secondend; and a number of screw bores defined through said plate between saidlower and upper surfaces and adapted to receive spinal screwstherethrough; a holder-drill guide, including;a first arm and a secondarm, said first arm attached to said second arm, each said arm having aproximal end and a distal end; a first foot attached to the proximal endof said first arm and a second foot attached to the proximal end of saidsecond arm, each said foot defining a number of thru-holes sized toreceive a drilling tool, each said hole being disposed in alignment witha screw bore in the spinal plate when the tool is engaged to a spinalplate; a hook attached to each said foot, said hook defining a surfacefor engaging an edge of the spinal plate; and a locking mechanismconfigured to lock said feet in a position relative to each other toengage the spinal plate between said hook of each said foot with saidthru-holes aligned with the plate screw bores.
 9. The system of claim 8,further comprising:a number of double-headed fixation pins, each saidpin having:a first head having a diameter greater than the diameter ofthe thru-holes in the feet; a second head having a diameter greater thanthe screw bores in the plate but smaller them the diameter of thethru-holes in the feet; a neck portion connecting the first and secondheads; and a shaft portion having a first end attached to the secondhead, said shaft portion sized for insertion through the thru-holes inthe feet, and a second end tapering to a point for insertion into thevertebra.
 10. The system of claim 8 wherein each end of the platedefines a notch on the lower surface of the plate for receiving the hookon each foot.
 11. The system of claim 8 wherein said plate has a pair ofscrew bores defined at both of said first and second ends between saidlower and upper surfaces and displaced from each other transverse tosaid longitudinal axis of the plate, said pair of screw bores havingcenterlines that diverge relative to each other below said lower surfaceof said plate; andsaid thru-holes in said feet diverge relative to eachother to align with said centerlines of said screw bores.
 12. The systemof claim 11 wherein:each of said screw bores includes a spherical recessdefined in said plate from said top surface; and said second head of thedouble headed pin is sized and shaped to be received within said recess.13. A holder drill guide tool for accurately drilling fixation holesinto vertebrae to be instrumented with a spinal plate having screwbores, the tool comprising:a pair of feet each having:a number ofthru-holes, each said hole disposed in alignment with a screw bore in aspinal plate when the tool is engaged to the spinal plate; a hookattached to each said foot, each said hook defining a surface forengaging an edge of the spinal plate; and a locking mechanism configuredto lock said feet in a position relative to each other to engage thespinal plate between said hook of each said foot with said thru-holesaligned with the plate screw bores.
 14. A method for accurately drillingfixation holes into vertebrae and instrumenting the vertebrae with aspinal plate, comprising:mounting a spinal plate against a surface of avertebral body, said plate having a number of screw bores therethrough;attaching a holder-drill guide tool to said spinal plate, the toolhaving a number of thru-holes therethrough, each of said thru-holesaligned with one of said plate screw bores; placing a drill-tap sleevein one of said thru-holes in said tool; drilling the vertebra throughsaid sleeve and screw bore; removing said sleeve and guide from saidplate; and seating a bone screw through said screw bore in said plate.15. The method of claim 14, wherein said tool includes:a number of feethaving a number of thru-holes; and a locking mechanism configured tolock said feet to said spinal plate and further wherein the step ofattaching the holder-drill guide tool to the spinal plate includesengaging the feet to the spinal plate with the thru-holes aligned withthe screw bores in the plate and locking the feet together about theplate.
 16. The method of claim 15, wherein the step of attaching theholder-drill guide tool to the spinal plate further includes mountingsaid spinal plate against the surface of the vertebral body with a hookattached to an edge of each said foot.
 17. The method of claim 14,wherein the step of attaching the holder-drill guide tool to the spinalplate includes extending a number of double headed fixation pins throughthe aligned thru-holes and screw bores and into the vertebra, thefixation pins having;a first head having a diameter greater than thediameter of said thru-holes in said feet; a second head having adiameter greater than said screw bores in said spinal plate but smallerthan the diameter of said thru-holes in said feet; a neck portionconnecting said first and second heads; and a shaft portion having afirst end attached to said second head and a second end tapering to apoint.